The present disclosure relates to swivel mechanisms for furling sails. Particularly, this disclosure relates to a lightweight swivel mechanism having a zero moment.
Sailing yachts are outfitted with equipment that enables sails to be handled easily in an automated fashion by a minimal number of crew members. Automation of the sail systems is important due to the size of the sail systems, and relatively small number of crew members. Large sailing yachts, with lengths in excess of one hundred feet, employ sailing systems which undergo dynamic load patterns and forces of considerable magnitude. The load patterns and forces are distributed throughout the sail system from the hull to the masthead. In general, the forces distributed throughout the sail system can be directly related to the square of the apparent wind velocity. Forces that a sailplane and sails resist can be estimated as the product of the squared apparent wind velocity and the total sail area of the yacht.
In conventional yacht design, the efficiency of the sail constitutes a major component of the total efficiency of a sailplane. The sail and tackle that enable the attachment of the sail to the yacht as well as the overall ability of the sail to be handled, adjusted and trimmed, must be engineered to function correctly and safely without mechanical failure.
One component within the sail system located at the top of the sail furling-luff-groove device is a sail swivel mechanism. The sail swivel mechanism is relatively small but undergoes extremely high loads. The sail swivel mechanism is a sophisticated piece of equipment located between a halyard and a head of sail, which enables automatic furling of the sail. The sail swivel mechanism prevents unwanted twisting and binding of the halyard and the head of sail as well. The clasps used to attach the head of sail to the halyard can deform or even fail through fatigue resulting from the stresses that the head of sail undergoes in combination with exposure to weather.
Since the sails aboard a yacht are so large, it is advantageous to eliminate the need to raise and lower the sails. The luff-groove mechanism is designed to rotate around a headstay for furling or unfurling the sail. The luff-groove is controlled by a furling drum and a synthetic line, or is controlled by hydraulic means having no lines and drum. The luff-groove mechanism turns the luff-groove in a clockwise or counter-clockwise direction. By the rotation of the luff-groove, the sail is driven to furl (wrap around the rotating luff-groove) or to unfurl (un-wrap from the luff-groove).
The luff-groove mechanism is often an aluminum tube or carbon fiber and epoxy laminated tube that carries a groove or tunnel on the aft side of the tube. The groove has an inside diameter of about one-quarter of an inch. The luff-groove mechanism is located and extends between the deck and the upper mast (headstay). The groove receives the sail along the length of the groove. The sail includes a rope or cylindrical section of material within the front or forward edge of the sail. The cylindrical section is inserted into the groove of the luff-groove mechanism and provides for the attachment of the sail to the luff-groove mechanism along the entire height of the luff-groove. The sail extends along its full length in the luff-groove.
The sail is raised (or lowered) in the luff-groove by a halyard to the upper section of the mast proximate to the headstay. Once the sail is raised, the sail can be furled about the luff-groove and stored until required for use. The luff-groove rotates as the sail is furled or unfurled. However, it is undesirable for the halyard to twist or rotate during the furling or unfurling process because the halyard and associated tackle can become damaged. The halyard is inhibited from rotating and twisting upon itself by the swivel mechanism, thereby preventing damage to the halyard and associated tackle.
It is thus required for the swivel mechanism to prevent the halyard from twisting and binding while maintaining resistance to the extreme forces applied to the sail during use of the sail. The extreme forces are translated from the sail to the swivel and the luff-groove. The forces are then translated to the headstay and halyard from the swivel and luff-groove. As a result of the forces through the swivel mechanism, moment arms (or simply moments) are created that place the swivel under great stress. These moments can also be translated to the luff-groove and halyard. Undue wear and ultimately failure of the components can occur as a result of the loads from the moments. Additionally, it is desirable to minimize the weight of the components above the waterline, including the components at the masthead like the swivel mechanism.
Therefore, there is a need in the sail furling art to have a swivel mechanism that is lightweight and reduces the moment applied to the components of the sail system.
The disclosed device is directed toward a furling swivel mechanism. The swivel mechanism comprised a liner defining a vertical centerline. An inner sleeve is disposed on the liner and the inner sleeve defines an inner sleeve recess. An outer sleeve is rotatably coupled to the inner sleeve and the outer sleeve defines an outer sleeve recess. A headsail yoke is coupled to the inner sleeve recess. A halyard yoke is coupled to the outer sleeve recess. The inner sleeve recess and the outer sleeve recess are configured to form a zero moment along the vertical centerline.
In another embodiment, the disclosed device is directed toward a furling swivel mechanism comprising a zero moment.
A method is disclosed for maintaining a zero moment for a furling swivel mechanism including an inner sleeve recess retaining a head of sail yoke and an outer sleeve recess retaining a halyard yoke. The method comprises translating a moment about the inner sleeve recess to a vertical centerline of the furling swivel mechanism. The method includes translating another moment about the outer sleeve recess to the vertical centerline of the furling swivel mechanism.